Some communication systems make use of multiple antenna elements at the transmitter and/or the receiver. For example, MIMO systems involve communication between a transmitter with multiple antenna elements and a receiver with multiple antenna elements. MIMO systems may offer spatial multiplexing, diversity, and beamforming gains compared to systems with a single antenna element at the transmitter and the receiver.
In massive MIMO communication systems, base stations may make use of arrays of antenna elements. The number of antenna elements is larger than a number of parallel streams being transmitted. For example, a multi-user (MU) massive MIMO system may have a base station with hundreds or even thousands of antenna elements simultaneously serving tens of users on a same time-frequency wireless resource.
Massive MIMO may increase the capacity and radiated energy-efficiency of a communications system. The capacity increase may result from aggressive spatial multiplexing. The energy-efficiency increase may result from coherent superposition of wave-fronts emitted by the large number of antennas to focus energy into small regions of space. By shaping the signals transmitted by the large number of antennas, a base station may aim to have wave-fronts collectively emitted by the antennas to add up constructively at the locations of intended receiver terminals, and destructively (or randomly) in other locations.
In some cases, the spectral efficiency of a massive MIMO system can be increased if the antenna elements and the transceiver at a base station allow full-duplex communication. Full-duplex communication involves simultaneous transmission and reception over a same wireless resource.
The channel quality of a wireless resource may vary over time. In full-duplex communication systems, self-interference between signals transmitted by a base station and signals received by the base station may negatively affect the channel quality of the wireless resource.